Trypanosoma cruzi is an obligate intracellular protozoan parasite. In mammalian hosts T. cruzi cycles between a trypomastigote stage which circulates in the blood and the amastigote stage which replicates in the cytoplasm of infected host cells (primarily muscle).
T. cruzi is the etiological agent of Chagas disease and is ranked as the most serious parasitic disease in the Americas, with an economic impact far outranking the combined effects of other parasitic diseases such as malaria, schistosomiasis, and leishmania (Dias et al., Mem. Inst. Oswaldo Cruz, 1999, 94:Suppl.1:103). Chagas disease is prevalent in almost all Latin American countries including Mexico and Central America, where approximately 18 million people are infected with T. cruzi and roughly 50,000 children and adults die of chronic Chagas disease every year due to lack of effective treatments. More than 90 million are at risk of infection in endemic areas. Additionally, 2-5% of fetus carried by infected mothers in endemic areas are either aborted or born with congenital Chagas disease. Loss of revenue in terms of productivity lost due to sickness and medical costs have an overwhelming effect on economic growth of these countries.
Recently, due to migration and immigration trends, T. cruzi has spread beyond the borders of Latin America and has been detected in Europe, Asia, and the United States (Ferreira et al., J. Clin. Micro., 2001, 39:4390). In the U.S., 50-100 thousand serologically positive persons progressing to the chronic phase of Chagas disease are present, and the number of infected immigrants in developed countries is increasing. It is expected that, due to the exponential increase in emigration from Latin America, Chagas disease may become a serious health issue in North America and Europe in the next decade.
As a result of the increase in the number of infected individuals, the risk of transmission of T. cruzi to non-infected individuals through blood transfusion and organ transplants from the infected immigrant donors is emerging as a route of T. cruzi transmission in more developed nations (Umezawa et. al. J. Clin. Micro., 1999, 37:1554; Silveira et. al. Trends Parasitol., 2001, 17; Chagas disease after organ transplantation—United States, 2001; MMWR Morb Mortal Wkly Rep. 2002 Mar. 15; 51(10):210-2). Each year, 15 million units of blood are transfused and approximately 23,000 organ transplants are performed in the United States alone, and presently almost none of the blood supply is tested for T. cruzi. A few cases of infection by T. cruzi through organ donation have already been reported to United States Centers for Disease Control since 2001. It has therefore become apparent that the screening of blood and organ donors is necessary not only in Latin America but also in developed countries that receive immigrants from endemic areas.
The most widely accepted serological tests for T. cruzi infection utilize antigens from either whole to semi-purified parasite lysates from epimastigotes that react with anti-T. cruzi IgG antibodies. These tests show a degree of variability due to a lack of standardization of procedures and reagents between laboratories, and a number of inconclusive and false positive results occur due to cross-reactivity with antibodies developed against other parasites (Nakazawa et. al. Clin. Diag. Lab. Immunol., 2001, 8:1024). Others report positive PCR and clinical disease in patients with negative serology. Salomone, et al. Emerg Infect Dis. 2003 December; 9(12):1558-62. A diagnostic test that is able to reduce the rate of false-positives while simultaneously enhancing sensitivity is urgently needed.